Pond Dynamics and Supraglacial-Englacial Connectivity on Debris-Covered Lirung Glacier, Nepal

Abstract

The hydrological systems of heavily-downwasted debris-covered glaciers differ from those of clean-ice glaciers due to the hummocky surface and debris mantle of such glaciers, leading to a relatively limited understanding of drainage pathways. Supraglacial ponds represent sinks within the discontinuous supraglacial drainage system, and occasionally drain englacially. To assess pond dynamics, we made pond water level measurements on Lirung Glacier, Nepal, during May and October of 2013 and 2014. Simultaneously, aerial, satellite, and terrestrial orthoimages and digital elevation models were obtained, providing snapshots of the ponds and their surroundings. We performed a DEM-based analysis of the glacier's closed surface catchments to identify surface drainage pathways and englacial drainage points, and compared this to field observations of surface and near-surface water flow. The total ponded area was higher in the pre-monsoon than post-monsoon, with individual ponds filling and draining seasonally associated with the surface exposure of englacial conduit segments. We recorded four pond drainage events, all of which occurred gradually (duration of weeks), observed diurnal fluctuations indicative of varying water supply and outflow discharge, and we documented instances of interaction between distant ponds. The DEM drainage analysis identified numerous sinks >3 m in depth across the glacier surface, few of which exhibited ponds (23%), while the field survey highlighted instances of surface water only explicable via englacial routes. Taken together, our observations provide evidence for widespread supraglacial-englacial connectivity of meltwater drainage paths. Results suggest that successive englacial conduit collapse events, themselves likely driven by supraglacial pond drainage, cause the glacier surface drainage system to evolve into a configuration following relict englacial conduit systems. Within this system, ponds form in depressions of reduced drainage efficiency and link the supraglacial and englacial drainage networks.

Mapping Surface Temperatures on a Debris-Covered Glacier With an Unmanned Aerial Vehicle

“…Thirdly, thermal UAV imagery could be applied in understanding the surface and subsurface hydrology. Englacial hydrology likely plays a key role in the drainage and transport of melt water through the glacier to the outlet (Miles et al, 2017), but the drainage paths are complex and difficult to measure. With a combination of thermal imagery, optical imagery, and the high-resolution DEM, it may be possible to infer supraglacial (sub-debris) and englacial drainage patterns.…”

The State of Remote Sensing Capabilities of Cascading Hazards Over High Mountain Asia

“…Meltwater storage on debris-covered glaciers varies seasonally and inter-annually. Some ponds coalesce and persist, whereas others drain seasonally upon interception with englacial conduits (Benn et al, 2012;Miles et al, 2017;Watson et al, 2017). Inhibited meltwater drainage leads to supra-and en-glacial water accumulation, and an increased likelihood of sporadic drainage.…”

Evolution of Glacial and High-Altitude Lakes in the Sikkim, Eastern Himalaya Over the Past Four Decades (1975–2017)

“…The sub-aqueous calving occurred in supraglacial lakes could also lead to collapse of roof of englacial conduit which would accelerate the ablation process (Sakai et al, 2000;Benn et al, 2012). The backwasting of exposed ice-cliffs bordering the SGL also contribute significantly in the ablation process (Thompson et al, 2016;Miles et al, 2017). Thompson et al (2016) found that despite of small total area (5% of total ablation area), backwasting of ice-cliffs contributed to 40% in total mass loss in Nojumpa glacier.…”

“…Owing to the sizable impacts of glacial lake development, expansion and outburst, this field of cryospheric sciences has seen tremendous upsurge in research, which in turn has led to much better understanding of the controlling factors and mechanisms involved in evolution of the glacial lakes (Reynolds, 2000;Benn et al, 2012;Westoby et al, 2014;Thompson et al, 2016;Miles et al, 2017). Moraine-dammed lakes typically develop in overdeepened glacier bed behind the lateral and terminal moraine that were formed during the Little Ice Age (Benn et al, 2012;Westoby et al, 2014).…”

“…Consequently, absorption of more radiation facilitates further melting (Reynolds, 2000;Benn et al, 2012;Thompson et al, 2016). Additionally, lakeshore ice cliffs are important for the mass balance of glaciers (Thompson et al, 2016;Miles et al, 2017), (iii) given an appropriate trigger (ice and rock avalanches, landslides, seismic activity etc. ), the moraine/ice dammed proglacial lakes may produce catastrophic Glacial Lake Outburst Floods (GLOFs).…”